1. Field of the Invention
The present invention relates generally to apparatus and methods for recording and analyzing the route traveled by a movable object. In particular, the present invention relates to an apparatus for use with a global positioning system, to methods for programming and using the apparatus, and to methods for recording and analyzing data obtained with the apparatus.
2. Discussion of Background:
Satellite-based global positioning systems were originally developed by the United States and the former Soviet Union as navigation aids for land vehicles, aircraft and ships at sea. At first, use of the systems--the United States Transit System and Global Positioning System (GPS) and the GLONASS system developed by the former Soviet Union--was largely confined to the military. Recently, however, decreases in the size and cost of GPS receivers have led to their increased use in civilian applications. (As used herein, the term "GPS" refers to a system of navigation satellites such as the GPS and GLONASS systems, both of which are now available for use by the general public of all nations.)
The United States GPS system has three segments: a space segment, a control segment, and a user segment. The space segment consists of twenty-five satellites in six low-earth orbits. The satellites constantly transmit signals with highly accurate orbital and timing information, including each satellite's range from the center of the earth. The control segment includes a master control station, several remote monitoring stations, and assorted uplink/downlink antennas. The monitoring stations track the satellites and feed the data to the control station, which updates the orbital information for each satellite and immediately transmits the updated data to the satellites.
The user segment includes a GPS receiver that receives the satellite signals and uses these signals to the calculate latitude, longitude, and altitude of the receiver by triangulation. The speed of the receiver is calculated by taking successive data points and computing the change in distance per unit time interval; the course is computed from the inverse tangent of the change in latitude divided by the change in longitude. Thus, a GPS receiver can determine its own three-dimensional position on the Earth's surface with a high degree of accuracy. When recorded and/or transmitted with the date and time for each position reading, this data can be used to plot the movements of an object (person; land, sea, or air vehicle; or indeed any movable object) with a high degree of accuracy. A GPS receiver with an on-board recorder can be viewed as analogous to the "black box" flight data recorders installed on airliners world-wide: like these instruments, it is capable of providing position, date, time, course, and speed data at regular intervals.
For military receivers, the GPS satellite system provides positional accuracy to within approximately 6 meters ("military accuracy"). For civilian receivers, there is a deliberately-induced error factor ("selective availability") that reduces the accuracy to .+-.100 meters, 95% of the time ("civilian accuracy"). Some civilian receivers are capable of accuracies on the order of .+-.30 meters, but significantly less than 95% of the time.
At present, civilian applications of GPS include personal navigation, commercial navigation, surveying, asset tracking, and many others. Some GPS receivers utilize a methodology known as Differential GPS (DGPS) to increase accuracy; some are capable of receiving both GPS and GLONASS signals.
GPS apparatus (that is, apparatus that includes a GPS receiver, a recorder, and associated circuitry) is widely available from several different manufacturers. However, much of this apparatus is expensive to manufacture, complex and difficult to use, and requires the services of a skilled technician to set the operational parameters of the instrument.
Furthermore, such apparatus only provides information relating to the position, time, course, and speed of objects. Such information is useful for applications such as navigation and asset tracking (of vehicles and other movable objects). For other applications, however, the positional data provided by a GPS apparatus must be correlated with data relating to other parameters of interest (presence and/or weight of cargo, the state wherein a moving vehicle is located, etc.). The availability of a self-contained apparatus that could record such additional data in conjunction with positional data would make GPS technology a useful management tool for a wide range of applications. However, no such apparatus is known.
There is a need for a compact, cost-effective, user-friendly apparatus with the capability for measuring environmental parameters of interest and integrating these measurements with the positional data provided by a GPS receiver.